This invention relates generally to packages for active microwave semiconductor devices and more particularly to packages of such type for use with the plurality of such active microwave semiconductor devices.
As is known in the art, active microwave semiconductor devices, such as p-i-n diodes and field effect transistors, are used in a wide variety of applications. In many of these applications, a pair of such devices are required. For example, in a microwave phase shifter, microwave energy is fed to a four port hybrid coupler. In such application, microwave energy is fed to an input one of the ports. A pair of p-i-n diodes terminate a corresponding pair of coupled ports. A load is coupled to an output one of the ports. The diodes may be biased to either a conducting state or a non-conducting state selectively in accordance with a DC (direct current) control voltage fed to appropriately forward or reverse bias the diodes. When microwave energy is fed to the input port and the diodes are changed from being biased from a first state, say a forward bias state, to the other state, say the reverse bias state, fed microwave energy coupled to the output port will correspondingly change in phase by 180.degree.. In order that the phase shifter operate over a relatively wide bandwidth, the terminations provided by the pair of diodes should have substantially matched impedances over the desired operating bandwidth.
As is also known in the art, one technique used to provide these substantially matched characteristic impedances is to electrically characterize (i.e. measure) the impedances of each one of a large quantity, or supply, of diodes. The diodes are then sorted into bins, each bin containing diodes having substantially matched impedances. Then during the assembly process, pairs of diodes from the same bin are mounted together to form a phase shifter. While this technique does result in the use of matched diodes for each phase shifter, when the diodes are actually bonded to form the phase shifter parasitics are introduced in the connecting leads, for example, which result in the mismatching of the impedances intended to be terminated by the diodes. Thus, additional compensation is required to achieve the desired matched impedance characteristics. This additional compensation process adds time and hence production cost in manufacturing the phase shifter.
As is further known in the art, the same phase shifter of the type described above sometimes requires that DC biasing of the diodes be accomplished using circuitry which is decoupled from, or electrically isolated from, the microwave frequency energy fed to and coupled from the phase shifter. That is, the DC voltages must "float" from the ground planes used for the microwave energy. One technique used to provide this isolation is to include a microwave series quarter wave stub, or sector, resonant circuit coupled between a junction connected to common electrodes of the pair of diodes and the ground plane. A DC voltage is also coupled to the common junction to bias the diodes, however, the capacitive element of the series resonant circuit provides the DC "block" or isolation between the common junction and the ground plane, yet such common junction provides, at microwave frequencies, a series short circuit between the common junction and the ground plane. Therefore, when the diodes are biased to a conducting condition, the common junction is at ground and thus, provides an effective short circuit condition to the microwave energy.
As is still further known in the art, it is sometimes desirable to provide a microwave phase shifter of the type described above which is adapted to operate with relatively high power. Thus, it is required to provide a heat sink for power otherwise dissipated by the diodes. In a strip line phase shifter of the type described above, the heat sink is provided by the outer ground plane conductors. Entrapped air (air gaps) between the ground plane conductor and the diode mounting mechanism may reduce the heat sink effectiveness of the ground plane conductor. Therefore, the means for mounting the diodes must be such that good mechanical contact is provided to the ground plane to achieve good thermal contact (that is, i.e. low thermal impedance) to the ground plane heat sink.